Amphibious construction equipment such as excavators and cranes is increasingly being used for construction where ground conditions are such that conventional heavy equipment runs a risk of being bogged down, in some cases irretrievably. The currently used amphibious equipment is custom-built and comprises the operative part of whatever piece of equipment is desired mounted on a pair of buoyant caterpillar-tracked pontoons so that the structure will not sink into soft ground. Making the equipment amphibious also allows it to be used in waterfront sites where access is difficult.
The pontoons carry sprocket-driven caterpillar tracks that allow the equipment to be maneuvered on land or water, the track sprockets normally being driven by hydraulic motors. Each track usually has two or more spaced sprockets on a driven axle and two or more spaced sprockets on an idler axle. The asymmetrical distribution of torque and traction between the front axle and rear axles limit the track efficiency especially when operating on highly undulating and viscous surfaces. Another undesirable effect is that tracks and motor will deteriorate more quickly because the unbalanced stresses generated by the idler and driven axles will lead to inconsistent metal fatigue in different parts of the tracks, and reduced the motor lifespan.
The prior art contains various proposals related to the train drive system of amphibious machines.
US-2005/0014425-A discloses a drive system for use in amphibious excavators and draglines having caterpillar-type treads or tracks. The system has an adjustable sprocket and chain connected between a final drive of an engine and a track axle that moves endless belts carrying the tracks or treads to propel the machinery. The improved drive system described in this document has a sprocket attached to the final drive of the motor; a sprocket removably affixed to a track drive axle near or at an end thereof, and an endless chain connecting the motor drive sprocket and the track drive sprocket. The sprocket and chain drive system can be adjusted to change torque and speed by removing and replacing the track drive sprocket with greater diameter sprocket for more track force and lower speed or with a lesser diameter sprocket for less track force and higher speed.
The result is an amphibious excavator with an improved tracking system, which uses multiple drive sprockets to suite the terrain condition. The improved tracking system allows the possibilities of sacrificing speed for torque and vice versa. Whilst allowing for different torque settings, the problems of motor and track deterioration and of inefficient torque to traction conversion are not addressed.
EP-1727687-B1 discloses an amphibious excavator which has a power transmission arrangement in the pontoon crawler track assembly, comprising an endless power transmission means in each of its pontoon members, such as chain formed by pin joints of successive formed parts that is arranged to be moveable by means of a wheel arrangement, such as a drive wheel and turnover wheel and/or support wheel arrangement or the like, on the outer periphery of the pontoon member, whereby each successive crawler track part of the crawler track arrangement is attached to the endless power transmission means. The pontoon crawler track assembly comprises a power transmission arrangement, essentially at the centre of each pontoon member, whereby each crawler track part of the arrangement is coupled with the power transmission means at its middle. The power transmission arrangement also comprises a chain tightening arrangement.
This document also fails to address the problems of motor and track deterioration and of inefficient torque to traction conversion.
One standard hydraulic drive train of existing amphibious construction equipment is powered by two hydraulic pumps. Each pump provides hydraulic pressure to a hydraulic motor on each side of a chassis. It also comprises a pair of parallel pontoons surrounded by a caterpillar track travelling round the periphery of each pontoon. The pressure from the hydraulic pumps is transferred to the hydraulic motors via fluid connections to provide power to two of the axles. The other two axles are idlers.
Other conventional amphibious equipment utilizes a single hydraulic motor in the drive train. Whether single of dual hydraulic motors are used they are selected based on the weight of the equipment. Higher capacity equipment requires more power for its operation and the only current solution is to employ either more powerful engines or bigger hydraulic motors. This correlation ultimately limits the range of motion of the upper structure or the mobility of the equipment depending on the placement of the motor.
This invention circumvents the various problems of amphibious construction equipment referred to hereinbefore.